Facebook's reported plans to open its doors to children under age 13 have sparked skepticism on Capitol Hill.

A Wall Street Journal report that the social media company is developing technology that could permit kids to sign up under adult supervision had some lawmakers voicing concerns about the potential privacy implications.

Reps. Ed Markey (D-Mass.) and Joe Barton (R-Texas) fired off a letter to Facebook, seeking to learn more about Facebook's work and the means by which it will obtain parental consent and use kids' data. One part of the missive went as far as to highlight the company's new status as a public company, and need to expand its market.

"We acknowledge that more and more children under the age of 13 are using Facebook and this is a problem that needs to be addressed," Markey and Barton wrote. "While Facebook provides important communication and entertainment opportunities, we strongly believe that children and their personal information should not be viewed as a source of revenue."

Markey and Barton want to know the sort of information Facebook might collect, and how it might use that data to target advertisements. In their letter, they asked whether Facebook’s exploration of new technology might lead it to consider implementing "Do Not Track" technology, and how it would handle users under age 13 who also access the site over a mobile device. The duo is seeking replies by June 25.

Facebook would face a daunting regulatory task if it tries to open its social network to youngsters. The Children’s Online Privacy Protection Act greatly restricts how companies collect and use personal data from kids under age 13. The law carries with it key requirements on how a company like Facebook would have to determine a child's age, and seek parental consent.

Currently, the FTC — the body overseeing implementation — is weighing updates to the statute, which was enacted in 1998.

For now, little is known of Facebook's plans: It has not actually announced anything, and the company may ultimately decide to abandon any new work. Yet the reported effort comes as the social media company continues to face criticism for the number of children lying about their ages — often, with the help of their own parents — to create profiles.

"Many recent reports have highlighted just how difficult it is to enforce age restrictions on the Internet, especially when parents want their children to access online content and services," a Facebook spokesman said Monday. "We are in continuous dialogue with stakeholders, regulators and other policymakers about how best to help parents keep their kids safe in an evolving online environment."

But lawmakers didn’t wait to register concerns.

Rep. Mary Bono Mack (R-Calif.), who chairs the House subcommittee that oversees the online privacy debate, warned Facebook to move carefully, hone its technology and inform parents of its new work.

"In developing this new technology, Facebook needs to proceed with an abundance of caution. Very strict privacy protocols must be in place before younger children are allowed on social networking sites,” Bono Mack said in a statement.

“Before this happens, Facebook also has a responsibility to expand its efforts to educate parents and preteens about the dangers of cyberspace and how to use the internet and social networking in a safe way," Bono Mack said.

Rep. Bobby Rush (D-Ill.) noted in his own statement Monday that any new offering would raise "significant privacy concerns and a number of questions." In particular, Rush wondered "how young is too young," and what sort of tools would be available to parents whose accounts are linked with those of their children.

This article first appeared on POLITICO Pro at 6:42 p.m. on June 4, 2012.